Pro-Tumorigenic Phosphorylation of p120 Catenin in Renal and Breast Cancer

Abstract

Altered protein expression and phosphorylation are common events during malignant transformation. These perturbations have been widely explored in the context of E-cadherin cell-cell adhesion complexes, which are central in the maintenance of the normal epithelial phenotype. A major component of these complexes is p120 catenin (p120), which binds and stabilizes E-cadherin to promote its adhesive and tumor suppressing function. However, p120 is also an essential mediator of pro-tumorigenic signals driven by oncogenes, such as Src, and can be phosphorylated at multiple sites. Although alterations in p120 expression have been extensively studied by immunohistochemistry (IHC) in the context of tumor progression, little is known about the status and role of p120 phosphorylation in cancer. Here we show that tyrosine and threonine phosphorylation of p120 in two sites, Y228 and T916, is elevated in renal and breast tumor tissue samples. We also show that tyrosine phosphorylation of p120 at its N-terminus, including at the Y228 site is required for its pro-tumorigenic potential. In contrast, phosphorylation of p120 at T916 does not affect this p120 function. However, phosphorylation of p120 at T916 interferes with epitope recognition of the most commonly used p120 antibody, namely pp120. As a result, this antibody selectively underrepresents p120 levels in tumor tissues, where p120 is phosphorylated. Overall, our data support a role of p120 phosphorylation as a marker and mediator of tumor transformation. Importantly, they also argue that the level and localization of p120 in human cancer tissues immunostained with pp120 needs to be re-evaluated.

A central role for cadherin signaling in cancer

“…Furthermore, the presence of the basolateral E-cadherin complex was required for the induction of these pro-tumorigenic signals, via SRC activation and p120 phosphorylation 152 . Consistent with these results, this and other studies have shown extensive and early loss of PLEKHA7 in breast and kidney tumors, whereas E-cadherin was still expressed to a large extend and p120 phosphorylation was also increased in tumors 152–154 . Collectively, these findings provided an explanation for the conflicting reports regarding the role of E-cadherin in anti- vs. pro-tumorigenic signaling.…”

Phosphorylation and isoform use in p120-catenin during development and tumorigenesis

“…Intriguingly, recent work on the whole genome level has indicated that Kaiso is largely associated with transcriptional activation as opposed to repression (Blattler et al, 2013); if this proves the case, it will be important to establish if p120 additionally has a role in this context. As part of earlier mentioned work, p120 phosphorylation at Y228 is predictive of glioblastoma multiforme (GBM) invasiveness (Huveldt et al, 2013), and is also elevated in invasive renal and breast tumors (Kourtidis et al, 2015). Further, T916 phosphorylation is high in these tumors; and while the functional role of phospho-T916 was not resolved, it was found to obstruct the epitope of the widely employed pp120 monoclonal antibody.…”

“…Recent work has furthermore identified DIPA as a binding partner specific for p120-isoform 1 (Klompstra et al, 2015; Markham et al, 2012; Markham et al, 2014), and an amino-terminal region preceding p120’s coiled-coil domain is an important binding site for kinesin (Figure 1). Given that other proteins associate with p120’s amino-terminal region, such as NLBP, PLEKHA7 and RPTPµ, future tests must assess the isoform specificity of these interactions (Chen et al, 2003; Kim et al, 2013; Kourtidis et al, 2015; Kurita et al, 2013; Markham et al, 2014; Meng et al, 2008; Pulimeno et al, 2010). …”

“…Utilizing phospho-specific antibodies, cancer cell lines have been evaluated to assess p120’s phosphorylation state (Mariner et al, 2004; Xia et al, 2006) (Table 1). E-cadherin contributes to determining p120’s phosphorylation in certain cancer cell types, presumably by recruiting p120 into complexes or regions rich in kinase activity (Kourtidis et al, 2015; Roczniak-Ferguson and Reynolds, 2003; Xia et al, 2006). …”

“…Rac1 and RhoA). This can occur while p120 is associated with or dissociated from the larger cadherin-catenin complex (Anastasiadis et al, 2000; Klompstra et al, 2015; Kourtidis et al, 2013; Kourtidis et al, 2015; Wildenberg et al, 2006). P120 can bind small-GTPases as a guanine-nucleotide dissociation inhibitor/ GDI (e.g.…”